Erasistratus was an ancient Greek physician and anatomist, active around the 3rd century BCE. He is often regarded as one of the founders of the field of physiology. Erasistratus made significant contributions to the understanding of the human body, particularly in the study of the circulatory system and the nervous system. He is known for distinguishing between arteries and veins, suggesting that arteries carry air rather than blood. Erasistratus was also a proponent of the scientific method, emphasizing observation and experimentation in medicine. His work influenced later physicians, including Galen, and laid the groundwork for future anatomical studies. His ideas were documented in various texts, although many of his works have been lost over time.